New and Modified Structures

In contrast to loss characters, new or newly modified structures are more likely to be unique synapomorphies that can be used to recognize clades in phylogenetic studies. Nonetheless, remarkable cases of convergence exist, provided that our phylogenetic hypotheses are correct. If our hypotheses are considered to be incorrect, worse problems of understanding phylogenies usually arise. The following are some examples of apparently new structures that seem to have arisen independently in different phyletic lines of bees.

The flabellum of the glossa in some species of Pa-nurginae, especially Perdita and various Calliopsini, resembles in detail the flabellum of many L-T bees (Figs. 28-1, 28-2, 86-1). The presumably ancestral bee glossa lacked a flabellum and had abundant long annular and seriate hairs, as in Melittidae, most Halictidae (Fig. 28-1a, b), most Andrenidae, and even a few colletid males. Distal enlargement of the glossa is found sporadically, weakly in Nomioidini (Fig. 28-1c), more strongly in Rophitinae (Fig. 28-1d-f). Even within the Panurginae, some genera lack such a flabellum-like structure, as shown by Protandrena (Fig. 28-2g). Others have a well-developed flabellum, as shown for Calliopsis in Figure 28-1i, j. Finally, in Perdita (Fig. 28-2h, i) the flabellum is essentially like that of L-T bees (Figs. 28-2a-f, 86-1). If the L-T bees arose from among the melittids, they had nothing to do with the Panurginae, and the flabellum as well as details of its structures arose independently. More information is given in Section 19. As also shown in Section 19, other aspects of glossal structure, for example large, divergent, seriate hairs, may have arisen independently, depending on the phylogeny that one accepts.

A remarkable feature that crops up occasionally in all major families is hairs on the eyes. It characterizes no tribe or higher-level taxon except Apini, but is usually characteristic of a few species, a subgenus, or sometimes a genus. Examples are as follows: a few species of Leioproctus (Col-letinae); Parapsaenythia (Panurginae); Agapostemon (Aga-postemonoides), Caenohalictus, Rhinetula, and some other Halictini; Caenaugochlora (Augochlorini); most Coe-lioxys (Megachilini); two subgenera of Pachyanthidium (Anthidiini); some species of Holcopasites (Ammobatoi-dini); Trichonomada (Brachynomadini); Trichotrigona (Meliponini); and Apis (Apini). As can be seen from this list, hairy eyes can be found in social as well as solitary bees, in cleptoparasites as well as nonparasitic forms—no functional explanation for the repeated origin of hairy eyes is evident. In Apis the eye-hairs are reported to monitor air flow, but why should a scattering of other bees have the same structure?

The ancestral thoracic shape for bees is cylindrical, with the scutellum, metanotum, and basal area of the propodeum horizontal or slanting (Figs. 20-5b, 28-3b). In a few taxa that live in narrow burrows in wood, this is also a derived state, sometimes accentuated, no doubt related to providing the elongate, slender body needed to use such nest burrows. Such cases include Chelostoma, Heriades, and Osmia (Pyrosmia) cephalotes Morawitz

(Megachilidae); and Ceratinini and Allodapini. Hylaeus (Heterapoides) (Hylaeinae) (Fig. 28-3a) is more elongate than other Hylaeus (Pl. 1), and is perhaps the most slender ofall bees. In many bees, however, the thorax is shortened by the propodeum becoming entirely vertical, sometimes also by the metanotum and even the posterior half of the scutellum likewise becoming vertical (Fig. 20-5a, c). The result is a nearly spherical thorax (Fig. 28-3c). All intermediates exist. Examples of bees with quite spherical thoraces are mostly in the Megachilidae and Ap-idae, but also occur in the Diphaglossinae (Colletidae) and Oxaeinae (Andrenidae). As was suggested by Mich-ener (1944), the spherical form is compatible with rapid and often hovering flight, and it is bees with such thoraces that exhibit such capability.

Danforth (1989a) has explained some of the convergent characters found in bee wings. Of course, there is a phylogenetic component as well; a moderately large stigma is clearly plesiomorphic relative to a minute stigma or a stigma that is essentially lost as in some Xylocopa, Cen-tris, and Oxaeinae. Nonetheless, there is a strong size-related component to wing characters, and even congeneric species, if of quite different sizes, may have conspicuously different wings. In minute forms the stigma is relatively large, the distal wing veins are often reduced and withdrawn from the apical region of the wing, and other wing veins and cells tend to be more transverse in the relatively shorter and broader wings. The converse features characterize wings of large bees. All this, of course, is related to aspects of flight mechanics. Since both large and small species occur in most families of bees, features characteristic of each size have arisen (and probably been lost) repeatedly during bee evolution. Illustrations throughout Sections 36 to 121 should be examined in this connection, but Figure 28-4 illustrates the wing shape and venation for three species of a single genus, Allodape, that are only moderately different in size (see the legend). When the wings are drawn the same size (length), as in this figure, the size- related differences are particularly conspicuous. See also Figure 41-1 for wings of small and large species of the genus Scrapter.

Large, fast-flying bees frequently have papillae on the distal parts of the wings, beyond the veins (Fig. 85-2a). They are present in bees as distantly related as Caupoli-cana (Colletidae), Centris and Eulaema (Apidae), and large Megachile (Megachilidae). Their presence is frequently associated with bare or partly bare wings, whereas most bees that lack or have only small papillae have rather uniformly, minutely hairy wings (Fig. 85-2b).

A curious relationship is common between the lengths of the basal antennal segments. In most bees the scape is much longer than the first flagellar segment, and the second flagellar segment is somewhat shorter than the first. In bees with a long flagellum, such as most male Eucerini, the first segment is shortened, often broader than long. Thus the longer the flagellum, the relatively if not actually shorter is its first segment (Fig. 112-8c-e). The few male Eucerini with rather short antennae have long first

flagellar segments; an example is Xenogkssa. There must be some mechanical reason for these regularly recurring relationships.

Males with unusually short antennae, although sometimes with the first flagellar segment long, are found among bees whose males form mating swarms or hover for long periods apparently in a mate-seeking context and have large eyes, convergent above. Presumably, the large eyes have to do with aerial pursuit of females. Such bees are Melitturga (Panurginae), Oxaeinae, some Exoneura (Allodapini), and Xanthesma subgenus Xenohesma (Eury-glossinae). Macrogalea (Allodapini) probably belongs in this list, although its male behavior is unknown. Some bees whose males have enlarged eyes and exhibit the relevant behavior described above do not have short antennae; examples are Apis and some Xylocopa..

A set of carinae or lamellae is widespread among bees, almost always in the same positions. Perhaps they have to do with strengthening the integument, but their positions are such that they might also have to do with defense of the neck, the metasomal base, and the bases of the antennae. They are (1) the juxtantennal carina beside and sometimes overlapping the antennal base, (2) the preoc-cipital carina, over and/or lateral to the posterior concavity ofthe head, (3) the carina ofthe pronotal lobe and dorsolateral angle of the pronotum, (4) the omaular carina,

Figure 28-4. Wings of Allodape. a, A. interrupta Vachal; b, A. ex-oloma Strand; c, A. mucronata Smith. Wing lengths are 5.6, 6.0, and 8.0 mm, respectively. Note that, from smallest to largest body and wing length, the stigma becomes relatively smaller and narrower, the wings become more slender, the veins labeled x in the first figure become more longitudinal and associated cells more elongate. From Michener, 1975b.

(5) the transverse carina on the scutellum, marking its posterior extension above the metanotum, and (6) the transverse carina of T1. Nearly all these are sometimes elevated to form lamellae rather than carinae. Some, most, or all of them are found in some colletines, especially Eu-lonchopria, in some Hylaeinae, and in some Apidae, and are especially common in Megachilinae.

Other structures probably serving for defense of the neck and petiolar regions are spines or angular projections on the dorsolateral pronotal angles, pronotal lobes, and axillae, and less commonly on other sclerites. Spines directed posteriorly and possibly protecting the metasomal base are especially diverse in Dioxyini, occurring in different genera on the posterior angles of the scutum, the axillae, the scutellum, and the metanotum (Table 83-1; Michener, 1996b). Angularly produced axillae occur in diverse bee taxa, such as most Coelioxys, some Heriades, some Stelis (all Megachilidae); some Callonychium (An-drenidae); and some Eulonchopria (Colletidae). For comments on these features and parasitism, see Section 8, under "Social Parasites and Cleptoparasites."

The inner hind tibial spur of females, described in Section 10, is ancestrally finely serrate or ciliate, to judge by its condition in sphecoid wasps. In many groups of bees, however, its inner margin is coarsely serrate to coarsely pectinate, and sometimes it bears only one large tooth or is even toothless. Figures 39-8, 66-13, and 67-5e-n illustrate various types. Especially diverse spurs are found in the Halictini, Augochlorini, and Colletinae; less diversity exists in certain other groups. I suspect that this structure has to do with combing pollen or, in some bees, oils, off the metasoma and perhaps other areas having scopal hairs as part of the unloading process in brood cells. Spurs are ciliate or finely serrate, i.e., like the plesiomorphic condition, in most parasitic bees (e.g., Temnosoma, Fig. 67-5e) and in nearly all males, although pectinate in a few males, e.g., Chlerogas(Augochlorini). Pectinate spurs must have arisen independently and probably also been lost in many groups of Leioproctus and other Paracolletini, various Eu-ryglossinae, diverse genera or subgenera of Halictidae, and some Apidae such as Tetrapedia. The especially finely pectinate spurs of Ctenoplectra (Apidae) presumably are used in manipulating floral oils; those of Tetrapedia may have the same function. Although not found in Mega-chilidae, the pectinate condition is approached in the coarse teeth of the outer margin of the same spur in Ash-meadiella femorata (Michener) (Osmiini) and its relatives. There are no data to suggest that the many female bees that do not have pectinate inner hind tibial spurs are less efficient in unloading pollen or oil than are those that have such spurs. It could be, however, that different kinds of pollen (sticky or dry, coarse or fine) are best manipulated with different kinds of spurs. Many species with pectinate spurs, e.g., most Halictini, however, are poly-lectic, not specialists on one or another type of pollen.

Figure 28-5. Hind tarsal claws of female of Xeromelecta californica (Cresson) (Melectini), dorsal and lateral views. The setae and the arolium are omitted from the lateral view.

The tarsal claws of various (but not all) cleptoparasitic Apidae have a distinctive form, the inner rami appearing as short, flattened blades whose apices are rounded or truncate, and the outer rami swollen basally and tapering, not much curved apically (Figs. 28-5 and 117-6; for comparison, see Fig. 10-10). This claw form has evolved in cleptoparasitic bees as dissimilar as some genera ofMelec-tini, Protepeolini, and Isepeolini ofthe Apinae and in various tribes of Nomadinae; its function is entirely unknown.

Many male bees have enlarged and sometimes grotesquely modified hind legs, but no major group of bees consistently has such legs; rather, some species of many genera are so equipped. They are particularly frequent in the Nomiinae and Xeromelissinae, but also occur with varying degrees of enlargement in Centridini, Colletinae, Emphorini, Halictini, etc. Presumably, such males use the legs to hold females at copulation. Such behavior has been described for Nomia (Wcislo and Buchmann, 1995). Toro and Magunacelaya (1987), working with Xe-romelissinae, described and illustrated the strong musculature occupying the swollen femora. Behavioral differences should be recognizable between related species with and without such legs. See also Section 4.

The preceding paragraphs describe only a sample of the new structures or arrangements that appear to have arisen independently among different bees. More examples can be gleaned from Michener (1944). An interesting case of specialized facial hairs of various species in diverse families, the hairs used for pollen collecting, is discussed in Section 6. The yellow facial marking of many male Hymenoptera is also probably a repeatedly derived feature; see Section 4.